In Watt, U.S. Pat. No. 3,936,557, are described blends of epoxide materials which, although essentially free of volatile solvents, are liquid and tractable for coating and related applications. The blends comprise epoxy prepolymers of the type glycidyl-bisphenol-A resins, epoxidized novolaks, polyglycidyl ethers, and alicyclic diepoxides, blended with bis(epoxycycloalkyl) esters. The compositions include a cationic polymerization initiator, in particular a radiation sensitive catalyst precursor, such as an aromatic diazonium salt of a complex halogenide. In use, the compositions are coated on a substrate, followed by the application of energy, through heating or through irradiation, to effect substantial polymerization of the epoxidic materials of the coating. A related, relevant disclosure is Schlesinger, U.S. Pat. No. 3,708,296. In Crivello and Schroeter, U.S. Pat. No. 4,026,705, it is disclosed that certain radiation-sensitive diaryl iodonium complex salts, such as diphenyliodonium hexafluoroborate, can be incorporated into epoxy resins to produce in one package radiation-curable compositions. Related teachings are found in Barton, U.S. Pat. No. 4,090,936. Such catalyst systems are more stable than the complex diazonium compounds. In Crivello, U.S. Pat. No. 4,173,551, diaryliodonium salts are disclosed to be effective thermal initiators for polymerization of epoxides when used in combination with various co-catalysts, such as copper salts. All of the foregoing patents are incorporated herein by reference.
It has now been found possible to formulate improved epoxide coatings if a novel and judicious choice is made of the type of epoxy compounds used, the type of catalyst employed, the amount of solvent used and the type and amount of pigment loadings employed. With the new coatings, no need of thinner reduction to application viscosity is necessary: Application can be made surprisingly easily at solids contents approaching 100 percent by weight. The coatings can be formulated, in general, with any conventional pigment and, if a tin salt is used, unique advantages in terms of room temperature cure rate will result. It is a principal object to provide the finisher with the option to totally eliminate the need for organic solvents. If the finisher still needs a solvent, the composition can still function with less than 10 percent by weight--which is well within Environmental Protection Agency regulations. As mentioned, it is remarkable that all these features are achieved at application viscosity, permitting the finisher to apply extremely heavy films with ease. In addition, as has also been discovered, the embodiments using tin salt co-catalyst will cure at room temperature. These unique and versatile coatings depend on the presence in the composition of the epoxide, the complex catalyst, the copper salt co-catalyst and the pigment, and such is the subject matter of this invention.